1. Field of the Invention
The present invention relates to LED driving circuits, and more particularly, to an LED driving circuit and an LED array device that can be directly used with AC power without using a conversion apparatus converting the AC power into DC power.
2. Description of the Related Art
Semiconductor light emitting diodes (LEDs) have advantages as light sources in terms of output, efficiency, and reliability. The research and development of the semiconductor LEDs that replace backlights of lighting apparatus or display devices as high-power and high-efficiency light sources has been actively conducted.
In general, light emitting diodes are driven at a low DC voltage. Therefore, an additional circuit (for example, an AD/DC converter) that supplies a low DC output voltage is required to drive a light emitting diode at normal voltage (AC 220V). However, the introduction of the additional circuit may not only complicate the configuration of an LED module, but also reduce the efficiency and reliability during a process of converting supply power. Further, an additional component except for a light source increases manufacturing costs and product size, and EMI characteristics are deteriorated due to periodic components during a switching-mode operation.
In order to solve this problem, various types of LED driving circuits that can be driven at an AC voltage without using an additional converter have been proposed. However, most of the LEDs are arranged so that they may be only driven in a predetermined half cycle of an AC voltage. This means the number of LEDs is increased in order to produce a desired amount of light.
The number of LEDs may vary according to the arrangement of the LEDs even when the same amount of light is supplied. The arrangement of LEDS according to the related art has very low efficiency. For example, when LEDs are connected in a reverse-parallel arrangement or a bridge arrangement, which is a representative arrangement in the related art, only 50% or 60% of the total number of LEDs actually emit light continuously. That is, the number of LEDs used is increased to obtain a desired level of emission, which reduces the efficiency.
Therefore, chip efficiency is required so that a smaller number of LEDS are used to produce the same amount of light by efficiently arranging the LEDs. In terms of economic efficiency, the chip efficiency is a very important consideration in the manufacture and sale of AC-driven LED circuits.
However, the chip efficiency is contrary to the reliability with respect to a reverse voltage. In general, the higher the chip efficiency is, the greater the reverse voltage is applied to LEDs in a half cycle during which the LEDs are not driven. The LED is vulnerable to the reverse voltage.
In particular, in a case of the LEDs that are essentially sensitive to ESD, the problem of the reverse voltage becomes even more significant. This needs to be carefully considered as well in order to increase manufacturing yield and ensure the use of commercial power is safe.